battery /alt issues.

Rebar · 08-05-2015, 07:26 PM

So I had alternator light come on, had alternator rebuilt, 1977 with external voltage regulator, did not replace it. I was able to charge my battery to 14 volts. It then went down over course of few days to 12.8. When I start the car with lights it goes down to 12.1. When I came back from a 20 min drive on highway it was 12.1 and when shut car off it was 12.5. Is everything OK? I have yet to keep driving it to see if it goes down past 12.1. Assuming it stays there do I have anything to worry about? Or should I just buy a new battery?
Second issue is when alternator was rebuilt it got new diodes and all and I think they might have replaced the piece with the shaft, maybe it is a little shorter, anyone have a measurement? There was a spacer on when I got it back and we are not sure if it came with it or not. The way the fan sits now it seems solid and lined up but I am only using about half the threads before it tightens down ( and don't worry they are they are not the issue it would not change much of anything). I did not take a picture of the nut on before and none of spacer or nut. I am thinking maybe it is a different nut that was used with 5 blade Gan the car came with because the thread wear/shinnyness seems to match to where I tight the nut down? Wrong nut or remove the spacer and see if that changes anything? By the way the alternator light is now out so I think everything is homed up correctly.
Thanks.

Rebar · 08-05-2015, 07:33 PM

Pic

Porboynz · Porboynz's Garage

The original nut is not as deep as the one pictured so I'm thinking its a replacement. The spacer is normal. The easiest test for a working alternator is to measure the voltage across the battery at idle and then again at 2000rpm. It should be at least 13 volts at 2000rpm, probably closer to 13.6 volts. If the voltage does not increase when the engine comes off idle and the light goes out then your alternator is not charging properly.

mboxler · 08-06-2015, 05:25 AM

Is it me, or is the belt inside out?

bob deluke · bob deluke's Garage

Looks inside out to me as well. Taper of belt should follow groove in pulley.

tkmoore · tkmoore's Garage

I'd say belt is on wrong and that it's likely slipping as a result. Once the belt is fixed, if the low voltage problem persists, it's very likely the external voltage regulator.

grizzfan · grizzfan's Garage

http://forums.pelicanparts.com/uploads24/Fan+nut1438828356.jpg

Agree with statements about your belt.

BUT The problem with your nut, I believe, is that the woodruff key down the shaft is not properly aligned. You really need to check that immediately or I can imagine all sorts of flying parts and damage.

Best.

Tom

Porboynz · Porboynz's Garage

Plenty of belts look like that one, optical illusion I think that makes it look inside out, it would never stay in place even if you could get it to fit the wrong way.

Avanti · 08-07-2015, 07:15 AM

Looks like on of those belts that have ribs on the outside apparently for cooling so they last longer.

Rebar · 08-07-2015, 05:11 PM

Hi guys thanks for the feedback. The belt is on correct , it is a dayco top cog belt with ribs one outside. Dayco® - Porsche 911 Series 1990 Top Cog

The woodruff key is sitting correctly, a few mm back from the edge of Tha fan hub. I will order a new nut. Anyone know the correct size?

I have not sold my electrical issue, or do I have one? I have not charged the battery and it is reading (without lights on or anything)12.4, doesn't really get any higher when I Rev it. I put in and old regulator that came in a box of stuff with the car and it is now running at 12.7, does not really go up when rev either, other than the .3 increase initially. When do I need to worry about it dipping down and having issue with driving, ignition? Maybe everything is fine and my battery is a little tired?

tkmoore · tkmoore's Garage

If your voltage regulator/alternator are charging correctly I believe that at idle it should give you a voltage reading close 13.5. Under a load ( with lights, wipers, etc. on) you should be getting 14.5 @2,000+ rpm.

Tim

Rebar · 08-07-2015, 06:25 PM

Really. Well I have certainly no gotten over 13v , the battery charged to 14.8 on the charger but by the time in got to running a few days later or a week it was down in the 12s. Good news is just came back from a spin and definitely getting a increase when I Rev it, but only from 12.2 up to 12.7. I guess maybe is should just buy the new optima battery I was going to get.